Seep water and groundwater at a phosphate mine contain up to 10 mg/L selenium (Se). PRIMA conducted batch and column tests to evaluate materials for a PRB, which is being considered as part of a long-term strategy to manage Se at the site. The proposed PRB media was a mixture of alfalfa, wood chips, and sand. We performed batch tests on each component to assess its potential to leach metals, then conducted multi-port column tests on the mixture to evaluate Se removal and estimate the hydraulic residence time (HRT) required to meet Se clean-up goals.
24-Hour batch tests confirmed that none of the individual materials should adversely affect water quality and demonstrated that Se could be removed under strong reducing conditions. Column tests demonstrated that a 24 hour HRT was needed to reduce Se in Seep water from 10 mg/L to 0.07 mg/L, which was very near the water quality goal of 0.05 mg/L. For Groundwater, an HRT of 3 hours was needed to reduce Se from 1 mg/L to below 0.02 mg/L. Column tests also confirmed that the PRB should not result in deleterious changes to other water quality parameters.
The results of this study were published in Journal American Society of Mining and Reclamation (JASMR) (Walker et al, 2018, 7(3), 20-44) and can be accessed from the “Peer-reviewed Papers” section of our Webinars, Presentations, and Papers page.